Five of the most elite types of tropical cyclones have formed in the Atlantic since 2016 — deadly Category 5s taking advantage of rich, gooey pockets of atmosphere to cultivate their fury.

It’s the first time in recorded history where Cat 5s have formed four years in a row. Two made landfall retaining the lofty crowns: 2018′s Hurricane Michael and this year’s Hurricane Dorian.

Scientists are reluctant to single out any one hurricane as the product of climate change. Before 2016, the Atlantic basin went eight years with no Cat 5s, and the king of all low pressure systems can be random, impulsive, firing up during wind shear lulls missed by forecasts.

But most researchers agree the conduct of these storms, including flooding rains, escalating intensities, and a swollen storm surge riding on rising seas, is consistent with what climate change models predict will happen more often as the world warms.


Will more storms sit on us and dump rain?


Emerging research also is looking at how climate change may breed some of the most damaging hurricanes:the ones that stall.

Left directionless by weak or shifting upper-air patterns, these types of storms, including Dorian, 2017′s Harvey and 2018′s Florence, batter the same area again and again with torrential rains and unrelenting wind.

“It’s kind of like your chickens coming home to roost. Dorian is all those things we predict; a rapid intensifier, it was a strong storm that maintained its strength for a long time, and it stalled,” said Jim Kossin, a climate scientist with the National Oceanic and Atmospheric Administration. “It’s a poster child for how bad things can get.”

The recent rash of Category 5 storms began with Matthew in 2016, followed by 2017′s Irma and Maria, 2018′s Michael and Dorian.

NOAA’s Geophysical Fluid Dynamics Laboratory recently issued a 20-page synopsis of current research results about global warming and hurricanes.

In summary, it says sea level rise, “which very likely has a substantial human contribution,” will cause higher coastal inundation levels for tropical cyclones. That means bigger waves and higher storm surge that reaches farther inland.


Climate change could mean storms will cause more destruction


Tropical cyclone rainfall rates likely will increase 10 to 15 percent within about 60 miles of a storm with 2 degrees Celsius, or 3.6 degrees Fahrenheit, of warming. (The Paris Climate Agreement aims to keep global temperature rise this century below 2 degrees Celsius above pre-industrial levels.)

The intensity of tropical cyclones likely will increase on average by 1 to 10 percent. The global proportion of tropical cyclones that reach very intense Category 4 and 5 levels also is likely to increase because of human-caused warming over the 21st century, according to the GFDL report.

“This change would imply an even larger percentage increase in the destructive potential per storm, assuming no reduction in storm size,” notes the report, titled “Global Warming and Hurricanes, An Overview of Current Research Results”, which was last revised Aug. 15.

But studies show the actual number of tropical cyclones will change little over the same time period.

“There is some disagreement in the scientific community on whether we’ll see more or fewer hurricanes in the future because we really don’t have a theory to tell us about hurricane numbers, but we do have a good theory on what the wind speeds will be,” said James Done, an atmospheric scientist at the National Center for Atmospheric Research. “We know hurricanes get their fuel from the ocean and the warmer the ocean, the more fuel there is.”

More than 90 percent of the warming that has happened on Earth over the past 50 years has occurred in the ocean, according to NOAA. Studies by the Intergovernmental Panel on Climate Change predict an increase in mean global ocean temperatures of between 1.8 and 7.2 degrees by 2100.

A warming atmosphere also holds more water, which means tropical cyclones will be heavy with torrential rains. Hurricane Florence dumped up to three feet of rain in some areas of North Carolina. More than five feet of rain fell in some areas of Texas during Hurricane Harvey.

“Studies have shown that between 20 and 50 percent of the rainfall in Hurricane Florence last year would not have occurred 30 years ago,” Done said.

What’s less clear is how much the increase in high-intensity hurricanes has already happened.

Lack of accurate hurricane data in the historical record, especially before the late 1960s when satellites were first introduced, muddies the number of hurricanes detected and their strength, said Phil Klotzbach, a hurricane researcher with Colorado State University.

There are 35 Category 5 hurricanes in records dating back to the 1880s, including the five since 2016.

“If you draw a straight line across hurricanes in history, you would say Cat 5s have gone through the roof,” he said. “The Atlantic was really active in the ’30s, ’40s and ’50s, and I suspect we missed some Cat 5s, especially if they were short-lived.”

Research planes didn’t start flying into storms until the mid 1940s, and then it might have been a single flight a day. In comparison, Dorian had nearly around-the-clock research planes testing it.

Klotzbach called Cat 5 hurricanes “stochastic,” or random, events. Weather Underground co-founder Jeff Masters agreed, noting that it’s rare for the National Hurricane Center to predict that a storm will reach Cat 5 status.

“Their attitude is these storms are so rare, and our tools for forecasting them are sufficiently unskillful, that it’s better not to forecast Cat 5 intensity in general,” Masters said.

Nascent studies on tropical cyclones in general are considering how global warming might be putting the brakes on the forward motion of hurricanes, which are steered like leaves in a stream by the weather patterns around them.


Ancient air patterns may also be disrupted by climate change


Lofty rivers of wind, such as the jet stream or the trade winds, are created by temperature differences between the frigid north and south poles of the earth and the balmy equator. As the poles warm faster than the tropical latitudes, the temperature gradient lessens.

Ancient equatorial air patterns that transport heat north to keep the earth’s energy budget balanced, such as the Hadley Circulation, may also be disrupted by a warming planet and have an effect on how hurricanes are steered.

Hurricane Dorian reached Grand Bahama at about 8 p.m. Sept. 1. It made landfall at 11 p.m. as a Category 5 storm with 180-mph sustained winds. It would remain nearly stationary through 8 a.m. Sept. 3. That’s an astonishing 36 hours that Dorian raged over Grand Bahama Island, nearly unmoving as a Category 5 or Category 4 hurricane.

A trough moving over the continental U.S. finally picked up Dorian and slowly began ushering it to the northwest. While most hurricanes average a forward speed of 15 mph, Dorian maintained an average of 1.3 mph over a 24-hour period when it tormented the Northern Bahamas, according to Robert Rohde, a lead scientist at Berkeley Earth.

Florence, which made landfall as a Category 1 storm, crawled along at just 2-3 miles per hour as a stagnant ridge of high pressure blocked its advance.

Kossin said he’s found a trend of about a 17 percent slowdown in the forward speed of hurricanes over the past 120 years.

“The slowdown in circulation patterns is supposed to continue through the end of the century,” Kossin said. “If we just keep doing business as usual, you could eventually have a storm that forms and would never move.”